Motor Torque and Speed dialog-box

This dialog is being updated ready for the next release 14.3

Email if you would like to know more.

Use Motor-Torque and Speed dialog-box to find a servomotor and gearbox that has the capacity to drive your cam mechanism.

Use this dialog-box to:

Select a Servomotor
Select a Gearbox
Show the Servomotor Torque and Speed: Maximum and RMS
Show the Gearbox Torque and Speed: Maximum and RMS
Find the Servomotor Duty Cycle as a percentage of the machine cycle
Upload your own database of Servomotors and Gearboxes.


You must do:

Visibility toolbar > Display Forces

... to see the Motor Symbol at the Pin-Joint in the graphic-area.

You must do

Configure Power Source

... to make sure the Torques and Speeds are correct.

To Open the Torque and Speed dialog-box


Make sure that these icons are 'active'

Forces toolbar > Calculate Forces and
Visibility toolbar > Display Forces Vectors

Makes sure that the power is assigned to the correct elements with:

Configured the Power Source

1.Double-click a Motor Symbol (see image).
- or -
1.Click the Motor / Pin-Joint in the graphic area.
2.Right-click the Pin-Joint in the Selection-Window.
3.Click Edit-element... in the contextual menu.

The Motor Torque & Speed dialog-box should open

Note: The first time you use this dialog in a session, MechDesigner loads the database of Motors and Gearboxes. Please wait for the database to open.


Select a Motor and Gearbox

Select a Motor Manufacturer and a Motor Part Number:

The Servomotor selection is made at the top and left of the dialog.

1.Click a Motor manufacturer - e.g. Parker

The box to its right will list the motors available from the Manufacturer

2.Click, in the list, a Motor Part-Number

To help you make a selection, we also show the Rated-Torque and Rated-Speed.

There are more parameters for the Motor in the database.

Select a Gearbox Manufacture and Gearbox Part Number:

The Gearbox selection is made at the top and right of the dialog.

1.Click a Gearbox manufacturer in the list - e.g. Wittenstein

The box to its right lists the gearboxes available from the manufacturer

2.Click, in the list, a Gearbox Part-Number

To help you make a selection, we also show the Gear-Ratio, rated-speed and Rated-Torque.

There are more parameters for the Gearbox in the database

The Torque-Speed Curve immediately updates each time you select a different motor or gearbox. Thus you can easily explore to find a satisfactory drive combination of motor and gearbox.

Note: You should check the parameters and your selection with your hardware supplier.

About the Torque / Speed and the Duty-Cycle Analysis Curves

X and Y Axes

Torque (N.m) is the Y-axis
Speed (RPM) is the X-axis

The Torque and Speed show four quadrants of Torque and Speed: ± Torque and also ± Speed .

Torque and Speed Graph Scales

Clear the 'Show Limit Lines' check-box:

The Torque and Speed graphs auto-scale to the maximum and minimum, even if the motor cannot deliver the Torque or Speed.

Select the 'Show Limit Lines' check-box:

The Torque & Speed graphs scale to the capacity of the Motor.

Points in the Graph

There points are at equal increments of the Master-Machine-Angle. The number-of-points is set in the Machine Settings dialog-box.

Thus, when the Torque or Speed, or both, change rapidly, the Points are further apart.

Point Colours

The Points have a colour code. The colours indicate whether the Motor or Gearbox, or the two, have the Torque and Speed capacity to drive the mechanism.

oGreen Points: the Motor & Gearbox have the Speed and Torque capacity in all respects.
oAmber/Orange Points: the Motor & Gearbox do not have the Continuous Torque or Speed capacity, or both
oRed Points: the Motor & Gearbox cannot provide the Torque or Speed, or the two.

Duty-Cycle Percentages

There are three Duty Cycle Plots

Power Duty Cycle
Torque Duty Cycle
Speed Duty Cycle

Each Duty Cycle Plot shows the distribution of the Power, Torque and Speed of the Motor for a complete Machine Cycle.

If you select 'Show Limit Line' check-box, then you can see if the motor must perform with more than its rated or maximum capacity.

If you want more detail for each chart, then increase the 'Bin Count'. You may also need to increase the number-of-steps in the Machine Settings dialog.

Kinetostatic Torque and Speed dialog-box

After you select a Motor and Gearbox, you can review the Torque and Speed.

Torque Speed tab

Click to Exapand or Collapse Torque Speed Curve of Servo-Motor, Four Quadrant, positive and negative torque and velocity
Click to Exapand or Collapse
Torque Speed Curve of Servo-Motor, Four Quadrant, positive and negative torque and velocity

Duty Cycle Analysis tab

Click to Expand or Collapse
Click to Expand or Collapse

The Database

Click Image to Exapand Collapse
Database for Drives, Motors, Gearboxes...

Click the Edit DB (Database) button

There are Six tabs


Ts = Stall Torque (Nm)

Tr = Rated Torque (Nm)

Tp = Peak Torque (Nm)

Wr = Rated Speed (RPM)

Jm = Motor Inertia (^2)

Ke = Voltage Constant (Vrms / 1000RPM)

Kt = Torque Constant (Nm/Amp)

R = Winding Resistance (Phase to Phase) (ohms)

L = Inductance (Phase to Phase) (mH)

Vmax = Maximum Voltage (V)

Frame Sizes
Gear Heads
Ball Screws

How to Import your own data into the database.

Step 1: Save the Old Database

Backup the original Database

This is typically in: C:\ProgramData\PSMotion\DBase\...

Step 2: Suppliers

1.Click the Suppliers tab
2.Click the 'tog_plus-red' , at the top
3.Enter with your keyboard a new:
Index number
Components (for example: Motors)

Step 3: Units

1.Click the Units tab

Check that the unit you will be using in your database is in the list of Units.

If the units you want to use are not, you can add a new Unit to the list.

2.Click the 'tog_plus-red' , at the top
3.Enter with you keyboard
Index number
Make the Quantity the same as another, unless you have a new 'Quantity'.
Make sure the UnitString is text, and does not not have spaces. For Example:
N . m = no ;
N.m = yes.
You must add the ratio to convert 'your' new unit to SI (System International) units.
Make this number as accurate as you need.


Step 4: Prepare the .CSV file.

The CSV file must include the text:

'Units' in Cell A3Red-14-1b
'Fields' in Cell A4

Row 3 must include the Units identical in text to the units in the Units Units tab - see Step 3

Row 4 must have the Fields the same as the Column Header in the tab to which you will append your new data.

An example .CSV File, the image shows:

Units 'N.m'.
This unit must be the same as in the Units tab in the database.
Field 'Ts'
This is the same as the Header 'Ts' in the Drives tab in the database.

If you do not have the particular data, for a Part, for example, Ke, then add zeros ('0') to the column in the .CSV File.

Step 5: Click the worksheet tab in the database in to which you want to import the .CSV data

Step 6: Import the .CSV File

The data in your .CSV file will append to the data in the database.

More information on Motor Torque and Speed

Why the Motor Torque is different to the Mechanism Torque

Why is the Motor Torque different to the Torque given at the Pin-Joint when you Display Forces with the Display Force Vectors tool?

The Torque we show in the graphic-area when we 'Display Force Vectors' is the torque to move only the mechanism.

It does not include the Torque to move the motor and gearbox. It is necessary to add the Torque to accelerate the motor and the gearbox to Torque in the graphic-area.

Clearly, the Torque to move motor depends on the ....motor and gearbox.

Each motor and gearbox has its own inertia, and efficiency.

The higher the gear ratio, the less Torque the motor 'sees'. But the motor must run faster and accelerate more itself.. This influences the overall power, as well as system efficiency.

Torque vs Speed Curves

The performance characteristics of a brushless servomotor (motor/drive combination) are described by a torque/speed operating envelope.

As shown below, the coloured areas of the curve identify the Exceeded Duty, Continuous Duty and Intermittent Duty zones of the system.

Exceeded Duty

To move the mechanical system, the gearbox and itself, the servomotor must exceeds its maximum speed or the maximum torque, or both.

Continuous Duty Zone

The continuous duty zone is bordered by the maximum continuous stall torque up to the intersection with the intermittent duty line. The continuous torque line is set by either the motor’s maximum rated temperature, or the drive's rated continuous current output, whichever is less.

The system maximum continuous or 'voltage line' is set by the voltage rating of the drives, the line voltage supplied, and the motor winding.

The system can operate on a continuous basis anywhere within this area, assuming the ambient temperature is 40°C or less.

Intermittent Duty Zone

The intermittent duty zone is bordered by the peak stall torque line and the system voltage line. The peak torque line is set by either the drives’ peak current rating, which the drive can give for a limited time, or the maximum rated peak current for the motor, whichever is less. Higher torque levels may be achievable at higher power levels.

Typical Torque / Speed Duty Capability of a Brushless Servomotor.

Typical Torque / Speed Duty Capability of a Brushless Servomotor.

Peak Torque: (ԎPS ) The Peak Torque the Motor and Gearbox at Stall Speed

Continuous Stall Torque: (ԎCS ). The Continuous Torque the Motor and Gearbox can give Continuously at Stall Speed.

Maximum Speed: (ωMAX ) Maximum possible speed of the Motor and Gearbox. Not attainable when the voltage is limited by the drive.

Knee Speed: (ωK ) The Speed at 'knee' in peak envelope that is the intersection of the Peak Torque with the Voltage Torque/Speed Limit Line.

Motor Providers also give a Rated Power - this is dependent on the Drive.

Continuous Rated Torque:(ԎCR ). The Continuous Torque at the Speed of the Rated Power.

Rated Speed: (ωR ) The Rated Speed or Speed at Rated Power. The motor can operate at this speed with the supply voltage.

How we calculate the Motor Torque and Motor Speed

The Reflected Inertia at the Motor shaft is usually continuously varying in a machine cycle.

With Constant Inertia Mechanical Systems it is easy to calculate torque.

With mechanisms, the torque is dependent on reflected inertia that is a function of Acceleration, Velocity, and Position.

PSMotion has developed algorithms to calculate these, which we believe give a true indication of the reflected inertia at a motor shaft for even the most complex mechanisms.

The equations below, are calculated at every instant in a machine cycle.

Typically, you aim to make the Reflected Load Inertia = (Motor + Gearbox) Inertia.

However, when the Load Inertia is not constant, it is more difficult to select the Motor and Gearbox.


ωm = N × ωL

αm = N × αL


Tm = - αm (JG + JM) + |TVD |

TL = (TMD / N ) / η

TT = Tm +  TL

N    = Gear Ratio

ωm = Motor Angular Velocity

ωL  = Load Angular Velocity

TT   = Total Torque

Tm  =  Motor Torque

TL  = Load referred to Motor Shaft.

TVD = Viscous 'Drag' Torque. It is added to the torque.

TMD = Torque derived by MechDesigner at the Motor Shaft ( f{PL , ωL, αL } )

JG   = Inertia of Gearbox

JM   = Inertia of Motor

αm  = Motor Acceleration,

αL =  Load Acceleration

η    = Gearbox Efficiency

Tutorials and Reference Help Files for MechDesigner and MotionDesigner 14.2 + © Machine, Cam, Mechanism, and Motion Design Software by PSMotion Ltd